Spiral compressor, useful in particular to generate compressed air for rail vehicles

ABSTRACT

In a totally oil-free spiral compressor (1) with high suction volume flows and compression ratio, useful in particular to generate compressed air for rail vehicles, the spirals are arranged on one side only and measures are taken to compensate for the high axial forces that act on the spiral bearings. Compression chambers (35) arranged with an axial gap between the spirals (7, 9) of the spiral compressor (1) are fed by compression pockets (45) and support the nested spirals against each other. The compression chambers (35) are preferably arranged between a compression crown (15) joined to the driving spiral (7) and a ring wheel (37) of the forcibly driven second spiral (9), so that axial counterforces compensate for the axial forces that act upon the bearings (29, 33) of both spirals.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates generally to a spiral compressor and morespecifically to totally oil free spiral compressor.

When generating compressed air, particularly when generating compressedair totally without oil for rail vehicles, special demands must be madeon the compressor technique because of the large amounts of air to begenerated and the extremely rough conditions. The full operating abilitymust always be ensured even under rough environmental conditions(temperature, vibrations, shocks, etc.).

In the field of rail vehicles, oil-free spiral compressors are receivingincreased attention, particularly for avoiding the occurrence of anoil-containing condensation and for simplifying the maintenance. Becauseof the capacity (for example, intake volume flow of approximately 1,600l/min.) which must be increased considerably in comparison to today'scommercially available, oil-free spiral compressors for rail vehiclesand the connected high stress to the spiral compressor, such compressorscannot merely be enlarged, particularly in view of the very high axialforces which have the tendency to press apart the spirals of thecompressor. In the case of a so-called one-sided spiral arrangement,particularly the support of such axial forces presents problems becausevery large bearings are required. These problems are becoming moreserious because of the required oil-free compression, because of whichthe friction output of the bearings is very difficult to achieve. Forthe above-mentioned reasons, compressors with a one-sided spiralarrangement have not been considered to be usable in the rail vehiclefield.

Based on the above, it is an object of the invention to further developa preferably completely oil-free operating spiral compressor with aone-sided spiral arrangement with a large intake volume flow as well asunder high compression conditions such that the above-mentioned problemsof high axial forces are taken into account. In particular, despite therequired volume and compression quantities, an operation of thecompressor is to be permitted which is free of high axial forces andthus as free of wear as possible.

The achieving of this object include in the case of a one-sidedarrangement of the spirals, specifically of the driving and of thepulled-along spiral, as a result of the pressure chambers fed bypressure pockets of the spiral compressor, a device is created in a verysimple manner by means of which the very high axial forces which actupon the bearings can be counteracted. A compensation of these axialforces can therefore be achieved. Despite the high rotational speeds ofthe two spirals, the function of the pressure chambers is ensuredparticularly in the case of dry running characteristics of the sealsbounding the pressure chambers since only a low relative speed existsbetween the spirals, thus also in the area of the pressure crown and ofthe ring wheel which, together with the pressure crown, forms thepressure chambers.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the invention will be explained by means of anembodiment with reference to the attached single drawing. This drawingis a sectional view of the spiral compressor according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawing shows a spiral compressor 1 which is provided with aone-sided spiral arrangement and which has an arrangement according tothe invention for compensating the high axial forces which act withrespect to the bearings of the compressor. The spiral compressor 1 isprovided with a housing 3 in which two meshing spirals extend,specifically one spiral 7 driven by a shaft 5 and one spiral 9 pulled bythe spiral 7. The two spirals each carry out a pure rotational movement.Because of the purely rotational movement of the spirals, there are noout-of-balance forces if the spirals are each balanced themselves out.

The relative movement of the two spirals with respect to one anotherrequired for a compression effect is generated in that the rotationalaxes 11 and 13 of the two spirals 7 and 9 respectively are offset.Furthermore, a pressure crown 15 reaches around the pulled-along spiral9, which compression crown 15 is fixedly screwed or otherwise connectedwith the driven spiral 7 (by way of fastening devices which are notshown). In order to ensure the function of the so-called "co-rotating"principle of the two spirals--that is, in order to ensure at any timethe correct relative position of the two spirals with respect to oneanother--an "antirotational mechanism" in the form of a forced guidanceacts between the two spirals. The antirotational mechanism consists, forexample, of three supporting rollers 17 which are carried by thepulled-along spiral 9 and which extend in bores 19 in the pressure crown15 which are arranged at the same angular distance from one another.Accordingly, three bores 19, are assigned to three supporting rollers 17arranged at an angular distance of 120° respectively with respect to oneanother. Since the pressure crown 15 rotates with the driven spiral 7,this spiral 7 takes the spiral 9 along by means of the walls of thebores 19 and the supporting rollers 17; that is this spiral 9 is pulledalong. In which case, because of the displacement of the axes ofrotation, within the degree of freedom of the bores, the two spiralscarry out "orbiting" movements with respect to one another. Theseorbiting movements of the spirals with respect to one another producebetween them spiral pockets which change in the volume and whichcontribute to the compression of the gas or air volume taken in by wayof an intake duct 21. The compressed air is pushed out of thecompression space 27 through an axial bore 23 situated in the center ofthe spiral 9 and by a pressure connection piece 25. The driven shaft 5of the spiral 7 extends in a bearing 29 while the shaft 31 of thepulled-along spiral 9 extends in a bearing 33.

In the case of a spiral compressor of the above-described one-sidedspiral arrangement, it is desirable for a completely oil-free runningthat a high compression ratio is achieved without pronounced stress tothe bearings because of the resulting axial forces on the spirals. Inorder to remedy this problem, an arrangement for compensating the axialforces is provided according to the invention. This arrangement consistsof pressure chambers 35 which are provided between the interior side ofthe pressure crown 15 and a ring wheel 37 mounted on the rear side ofthe spiral 9. In the illustrated embodiment, the pressure chambers 35are the very low volumes which exist in each case between the ring wheel37 and the facing interior surface of the pressure crown 15. The sizeand the shaping of the pressure chambers is determined by dry-runningseals 39 which seal off the pressure chambers with respect to outsideair; that is, with respect to the outside-air volume between the coolingair inlet 40 and the cooling air outlet 41 of the spiral 9. In theillustrated embodiment, three pressure chambers 35 are in each caseprovided at the same angular distance of 120° from one another situatedbetween the bores 19, the pressure chambers 35 are in each case suppliedby way of bores 43 with compressed air from the compression pockets 45of the spirals.

Because of the above-described pressure supply of the pressure chambers35, a pressure is built up in these pressure chambers during theoperation of the spiral compressor. The pressure presses the two spiralstowards one another because the pressure crown 15 is connected with thespiral 7 and the ring wheel 37 is carried in the rearward area of thespiral 9 by this spiral, for example, by radial cooling ribs 47connected with the spiral 9 or by the bearing pins of the supportingrollers 17 which penetrate the ring wheel 37 at an angular distance fromone another, as illustrated in the upper sectional half of the drawing.Since, by means of the above-described arrangement for the axial forcecompensation, the spirals 7 and 9 are pressed towards one another, thebearings 29 and 33 are relieved from axial forces to the same extent,which is why oil-free operating spiral compressors of the described typecan also operate at a high compression ratio in the case of a highintake volume.

In addition to the above-mentioned cooling air arrangement for thespiral 9, a corresponding cooling system is also provided on the spiral7; that is, there is a cooling air inlet 49 and a cooling air outlet 51.In addition, radial cooling ribs 53 are provided which are connectedwith the spiral 7.

We claim:
 1. An oil-free operating spiral compressor, used forgenerating compressed air for rail vehicles, having at least a first andsecond spirals which are arranged in a housing, extend in one another,are each carried by a bearing and whose relative movement with respectto one another required for the compression effect is generated by amutual displacement of their axes of rotation, for the purpose of thecompensation of the axial forces exercised by the spirals onto thebearings on the interior side of a pressure crown connected with thefirst spiral which extend in one another, pressure chambers are providedwhich, under the effect of pressure of the compressed air fed by thespiral compressor, press the two spirals towards one another for thepurpose of relieving the bearings whereina. the pressure chambers areformed between an interior side of the pressure crown and a ring wheelresting against the pressure crown, b. on a side facing away from thepressure chambers, the ring wheel is supported on radial cooling ribsconnected with the second spiral, and c. the pressure chambers are fedwith compressed air by way of bores extending through the cooling ribsand by way of passages in the ring wheel by compression pockets of thespiral compressor.
 2. An oil-free operating spiral compressor accordingto claim 1, whereina. the pressure chambers are each bounded by apressure chamber seal with dry-running characteristics embedded in thepressure crown, and b. the ring wheel overlaps the pressure chambers ata sliding speed corresponding to the relative speed between the twospirals.
 3. An oil-free operating spiral compressor according to claim 1wherein three pressure chambers are between the interior surface of thepressure crown and the facing interior surface of the ring wheel whichare at an angular distance of 120° respectively with respect to oneanother.
 4. An oil-free operating spiral compressor according to claim 1wherein the first spiral is driven and the second spiral is pulled alongby the first spiral by a forced guidance.
 5. An oil-free operatingspiral compressor according to claim 4, whereina. rotatably displacedsupporting rollers extend from the rear of the second spiral facing thepressure crown, and b. the supporting rollers are in bores which areentered into the pressure crown.
 6. An oil-free operating spiralcompressor according to claim 5, wherein three supporting rollers whichare arranged at angular distance of 120° with respect to one another onthe rear of the second spiral, extend away from the second spiral andeach roll in the bores of the pressure crown are connected with thefirst spiral.
 7. An oil-free operating spiral compressor according toclaim 5, wherein the supporting rollers and the pressure chambers arealternately arranged on a graduated circle.